1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier or a page printer, that includes a developing apparatus that employs electro-photography, for example, to form a latent image on an image bearing member, that develops the latent image using a developer transporting member that supplies a developer to develop an image. The present invention also relates to a cartridge, a storage device and a developer supply method.
2. Description of the Related Art
Conventionally, two-component developing apparatuses, which employ a two-component developer containing toner and a carrier, have been employed for image forming apparatuses. Recently, however, there has been increased use of one-component developing apparatuses, which employ developers, such as magnetic toner, having a single component and a simple composition. In addition, from the viewpoint that further improvements are desirable, service life has been extended and running costs have been reduced, and many one-component supply methods for supplying toner for one-component developing systems have been proposed.
Since a large amount of toner is contained in a developer container for a one-component supply system, this system is advantageous, in that a precise toner supply control process, such as that provided for a two-component supply system, is not required.
For a developing apparatus that employs this supply type, toner to be consumed for image forming is supplied, by a toner supply device, in order to maintain a constant toner level in the developer container. To accomplish this, one method has been proposed whereby a valve, provided in a developer container, mechanically maintains the toner level and another method has been proposed whereby a sensor, which also is provided in the developer container, detects the toner level and toner is supplied based on the detection results.
Furthermore, as described, for example, in Japanese Patent Laid-Open No. Hei 5-88554 or No. Hei 8-146736, a toner supply method that employs a video count value has been practically employed. According to this method, output signal levels for all pixels in a digital image are added together and a printing ratio is obtained for the image, and from this, the amount of toner consumed is calculated to determine how much toner is required to replenish the container.
FIG. 18 is a schematic diagram showing a configuration of a conventional image forming apparatus. In this example, a drum shaped, electrophotographic photosensitive member (hereinafter referred to as a “photosensitive drum”) 51, which serves as an image bearing member, is supported almost in the center of an image forming apparatus 100 and is rotated in the direction indicated by an arrow. When an image forming operation is initiated, an electrifier 52 uniformly charges the surface of the photosensitive drum 51, following which a laser irradiation unit 53, which serves as an exposing apparatus, exposes the surface of the photosensitive drum 51, in consonance with image data, and forms an electrostatic latent image thereon.
The electrostatic latent image is then developed by a developing apparatus 4, and a toner image is obtained. Then, a transferring field that is formed between the photosensitive drum 51 and a transferring roller 56 that serves as a transferring unit, the toner image is electrostatically transferred to a recording material P by a transferring roller 56. Thereafter, a fixing apparatus 58 employs heat and pressure to permanently fix the toner image to the recording material P.
Further, after the transfer of the toner image has been completed, residual toner on the surface of the photosensitive drum 51 is removed by a cleaning apparatus 57, for which a blade shaped cleaning member is provided, and the photosensitive drum 51 is thus prepared for the performance of the following image forming process.
The developing apparatus 4 includes a developer container 10, in which developer is contained; a developing roller 11, which is a developer carrier; a supply roller 13, for supplying developer to the developing roller 11; a developer regulation member 14, for controlling the amount of developer deposited on the developing roller 11; and an agitation member 15, for agitating the developer in the developer container 10. A developer supply apparatus 5 is provided above the developer container 10, and as the quantity of toner available in the developer container 10 is reduced, toner from the supply apparatus 5 is supplied, as necessary, to ensure the supply of toner available in the developer container 10 remains constant.
A toner supply method employing the video count measurement will now be explained while referring to FIGS. 15, 16 and 17. FIG. 15 is a block diagram showing the configuration of an apparatus for obtaining a video count. FIGS. 16A to 16D are explanatory diagrams for describing the process by which a video count is obtained. And FIG. 17 is a flowchart for explaining a toner supply operation.
For the image forming apparatus in FIG. 18, the exposing apparatus 53 is a laser scanner that includes a semiconductor laser, a polygon mirror and a lens (none of them shown). A laser beam is emitted by the semiconductor laser, passes though a lens, such as a f/θ lens, and is directed towards the photosensitive drum 51, as a spot, by a fixed mirror and is swept across the photosensitive drum 51, which is an image bearing member, by the polygon mirror. Thus, the laser beam scans the photosensitive drum 51 in a direction substantially parallel to the rotary shaft of the photosensitive drum 51, i.e., in the main scanning direction, and forms an electrostatic latent image.
While referring to FIG. 15, an image that will become an electrostatic latent image is transmitted by a PC, or an image scanner, via an image signal processing circuit 31, to a pulse width modulation circuit 32. Then, for each input pixel image signal, a laser drive pulse having a width consonant with the signal pulse (a time length) is formed and is output to the exposing apparatus 53. That is, as shown in FIG. 16A, for a pixel image signal having a high density, a drive pulse W having a wide width is formed; for a pixel image signal having a low density, a drive pulse S having a narrow width is formed; and for a pixel image signal having a middle density, a drive pulse I having an intermediate width is formed.
The laser drive pulse output by the pulse width modulation circuit 32 is transmitted to the exposing apparatus 53, which then emits a semiconductor laser during a period equivalent to the pulse width. Therefore, the semiconductor laser is emitted for a long period of time for a high density pixel, or for a short period of time for a low density pixel. Thus, for the high density pixel, the photosensitive drum 51 is exposed in the main scanning direction over the long range, and for the low density pixel, it is exposed over the short range. That is, the dot sizes of the electrostatic latent image differ depending on the densities of the pixels. Accordingly, the amount of toner consumed by a high density pixel is larger than is that consumed by a low density pixel. It is noted that L, M and H in FIG. 16B denote low, middle and high density pixels for an electrostatic latent image.
A signal output by the pulse width modulation circuit 32 is transmitted to one of the input terminals of an AND gate 34, and a clock pulse (a pulse shown in FIG. 16C) is transmitted by a clock pulse oscillator 35 to the other input terminal of the AND gate 34. Therefore, as shown in FIG. 16A, the AND gate 34 outputs a count of clock pulses in consonance with the pulse widths of the individual laser drive pulses S, I and W, i.e., the number of clock pulses consonant with the densities of individual pixels. For each image, the clock pulses are totaled by a counter 36, and the result is transmitted to a CPU 37 to obtain a video count. The video count, i.e., the exposure area is then employed to calculate an image printing ratio (an exposure area/paper area). Since the amount of toner to be consumed for image forming has a substantially linear relationship with the image printing ratio, the amount of toner that was probably consumed is predicted based on the image printing ratio, and a supply driver 38 is operated for the time required to replenish the container with toner.
The conventional toner supply operation performed by the image forming apparatus 100 will now be described while referring to FIG. 17. When a main body 100A of the image forming apparatus 100 is powered on (S1) and a predetermined activation process is completed, the image forming apparatus 100 becomes in the standby state (S2). When a print signal is received in the standby state, a printing operation is started (S3), and the photosensitive drum 51, the electrifier 52 and the developing apparatus 4 are sequentially activated (S4). When these apparatuses are about to time to be ready, the exposing apparatus is started to form a latent image, and at the same time, acquisition of video (pixel) count data is started. When the latent image has been formed, the exposing apparatus is halted, and video count totaling is also ended, to obtain a video count total (S5 to S7).
For image forming process, the CPU 37 that controls the operation of the image forming apparatus 100, employs a video count to calculate the amount of toner consumed, i.e., the amount of toner that must be added, and replenishes the toner (S8 and S9).
Thereafter, a check is performed to determine whether the job has been completed (S10). When the job has not yet been completed, and sequential printing is still required, the image forming apparatus 100 returns to step S5 and enters the next image forming cycle to activate the exposing apparatus 53. When there are no sheets remaining for the printing job, the individual apparatuses are halted in order, and the image forming operation is terminated (S10). The image forming apparatus 100 and then returns to step S2, and is set to the standby state.
FIG. 12 is a graph showing the relationship between the image printing ratio and the amount of consumed toner. That is, the image printing ratio and the amount of toner consumed are substantially proportional. In order to maintain a constant volume of toner in the developer container, the amount of toner to be supplied must only be equal to the amount of toner consumed. FIG. 13 is a graph showing the linear relationship between the image printing ratio and the amount of toner to be supplied.
When the above described linear relation is employed, the amount of toner to be supplied can be calculated in accordance with the video count. When the video count is small, the amount of consumed toner is also low, a small amount of toner need only be supplied by driving a toner supply mechanism for a short period of time. When the video count is large, the amount of consumed toner is also large, and a large amount of toner must be supplied by driving the toner supply mechanism for an extended period of time.
With this arrangement, at an appropriate timing, toner can be supplied in consonance with the amount of toner consumed, and a constant amount of toner can be maintained in the developer container. However, there is a case wherein the following problems occur in the above described operation.
Since a large amount of toner is consumed when image forming is performed at a high printing ratio, such as for solid black image printing, accordingly, the amount of supplied toner is increased. When the developer container is replenished with a large amount of new toner, there is no special problem, so long as the charging capability of the developing apparatus is satisfactory. However, in a case wherein the durability of the developing apparatus is lowered and the parts are deteriorated, or wherein the electrostatic property of toner is degraded due to the environment, such as a high temperature and a high humidity, when a large amount of new toner is supplied to the developer container, all the toner can not be fully agitated and charged, so that image fogging or toner scattering will occur.
When, as shown in example 1 in FIG. 14, the relationship between the image printing ratio and the amount of toner supplied is linear, the amount of toner supplied, at a high printing ratio of about 70 to 100%, would exceed the charging capability of the developing apparatus, and image fogging and toner scattering might occur.
Thus, conventionally, the relationship between the image printing ratio and the amount of toner supplied has been reviewed, and a method has been employed whereby, as shown in example 2 in FIG. 14, the inclination of a linear table is set so it is smaller, or as shown in example 3 in FIG. 14, the line indicated for the toner supplied at a high printing ratio is below the line in example 1 for the reduction in the supplied toner amount.
FIGS. 10 and 11 are graphs showing the above described examples 1, 2 and 3 for the shifting of the amount of toner supplied and the amount of toner in the developer container, when the printing of 1000 sheets was performed by changing the printing ratio from 5% to 100% every 100 sheets.
A value (a target value) that the amount of toner in the developer container is aimed at is defined as 150 g. At 130 g, a toner level Low alarm is generated by an optical sensor, and at 170 g, a toner level HI alarm is generated to perform a toner amount restoration sequence.
As understood by referring to Table 1 below, since in Example 1 an amount of toner equivalent to the amount of toner consumed is supplied each time, toner in the developer container is not lowered, as shown in FIG. 11. However, were a large amount of toner supplied during high-ratio printing, image fogging and toner scatting would occur.
TABLE 1Developer containerFoggingtoner volume LowExample 1X◯Example 2ΔXExample 3ΔX
In Examples 2 and 3, since a reduced amount of toner is to be supplied for high-ratio printing, image fogging and toner scatting can be prevented during the high-ratio printing. However, since the amount of toner supplied during high-ratio printing is insufficient, the amount of toner in the developer container is gradually lowered, and either a toner Low alarm for the developer container may be erroneously turned on, or the toner volume restoration sequence may be frequently performed.
As described above, it is very important, but is at the same time difficult, to resolve a problem that arises when toner can not be fully agitated and charged, while a large amount of new toner is being supplied during high-ratio printing, and a request is issued that the amount of toner in a developer container be maintained by accurately adding a required amount.